1. Field of the Invention
The present invention relates to an electrooptic probe (E-O probe) which is applied to a voltage measurement apparatus which measures the voltage of an object without contact by detecting electric field strength generated by the object.
2. Related Background Art
Techniques disclosed in "Japanese Patent Laid-Open No. 63-308572" have been known in the above-described field. In this reference, an E-O probe in which a metal reflecting film is formed on a measuring surface of an electro-optic material of which the refractive index is varied by a change of the electric field is disclosed.
Referring to FIG. 1 and FIG. 2, the measurement of the electric field strength by such an E-O probe will be explained. FIG. 1 and FIG. 2 show a perspective view and a side view, respectively. As shown in these drawings, the conventional E-O probe 100 comprises an electro-optic material 101, a reflecting film 102 which is a thin metal film fixed to an end face of the electro-optic material 101 facing to an electrode to be measured 110, and a transparent electrode 103 fixed to the other end face of the electro-optic material 101. The transparent electrode 103 is set at ground voltage level, or at a fixed voltage level. In a case of a thin electro-optic material 101, the E-O probe is used with the upper part of the transparent electrode 103 fixed by a transparent support 104.
In the conventional E-O probe, there were problems that the voltage of the electrode to be measured could not be measured at high sensitivity and that since the cut-off frequency f.sub.T against the voltage signal was comparatively high, the voltage signal at low frequency could not be measured.